Ductwork is often used for conveying conditioned air (e.g., heated, cooled, filtered, etc.) to or from a room or other areas within a building. Conventional ducts are made of sheet metal and have a substantially fixed internal volume regardless of whether the duct is conveying supply air to a room or return air from the room.
Sheet metal ducts are often installed above suspended ceilings for convenience; however, in warehouses, manufacturing plants and other industrial installations, it can be more practical and less expensive to install the ductwork underneath the ceiling. Sheet metal ducts underneath a ceiling, however, can create problems in those installation sites where prevention of air-borne contamination of inventory or other items is critical.
For instance, temperature variations in the building or temperature differentials between the ducts and the air being conveyed can create condensation on the interior or exterior of the ducts. The presence of condensed moisture on the interior of the duct may form mold or bacteria that the duct then passes onto the room or other areas being supplied with the conditioned air. In the case of exposed ducts, condensation on the exterior of the duct can drip onto the inventory or personnel below. The consequences of the dripping can range anywhere from a minor irritation to a dangerously slippery floor or complete destruction of products underneath the duct (particularly in food-processing facilities).
Further, metal ducts with localized discharge registers have been known to create uncomfortable drafts and unbalanced localized heating or cooling within the building. In many food-processing facilities where the target temperature is 42 degrees Fahrenheit, a cold draft can be especially uncomfortable and perhaps unhealthy.
Many of the above problems associated with metal ducts are overcome by the use of inflatable fabric ducts, such as DUCTSOX from DuctSox Corporation of Peosta and Dubuque, Iowa. Inflatable ducts typically have a pliable fabric wall (sometimes porous) that inflates to a generally cylindrical shape by the pressure of the air being conveyed within the duct. Fabric ducts seem to inhibit the formation of condensation on its exterior wall, possibly due to the fabric having a lower thermal conductivity than that of metal ducts. In addition, fabric porosity and/or additional holes distributed along the length of the fabric duct broadly and evenly disperse the air into the room being conditioned or ventilated. The even distribution of airflow also effectively ventilates the walls of the duct itself, thereby further inhibiting the formation of mold and bacteria.